Implantable infusions systems have been used to treat a variety of diseases, such as spasticity, pain and cancer by targeting drug delivery to a selected area of a patient. Therapies employing such systems have proven to be very helpful for patients for which systemic therapy is not effective, possible, or practicable. The implantable systems include an implantable infusion device containing a reservoir for housing the drug and a catheter coupled to the reservoir to direct the drug to the target area. The devices typically include a pump or mechanism for driving fluid from the reservoir, or withdrawing fluid from the reservoir, and through the catheter.
Many implantable infusion devices are configured to allow the reservoir to be transcutaneously refilled. Clinicians who refill the reservoirs of implantable infusion devices would benefit from an indication of reservoir “fullness” during the refill procedure. Such an indication may also increase conformance by ensuring that the reservoir repeatedly reaches a completely full status each time the reservoir is refilled.
Some implantable infusion devices have an over-pressurization mechanism (OPM) that prevents overfilling of the reservoir. The OPM may serve as a valve that closes an entry port into the reservoir when the reservoir is full. Closing the OPM valve results in increased pressure upstream of the valve, which can be felt by a clinician injecting fluid into the reservoir as increased resistance to syringe plunger advancement. This tactile feedback can be used by experienced clinicians as feedback that the reservoir has been filled.
However, due to manufacturing tolerances, the OPM valve is typically set to close when the reservoir is slightly beyond the desired fill level. As such, the OPM valve may not close every time that a reservoir is refilled. One way to ensure that the OPM valve closes is to reduce the reservoir volume at which the OPM valve closes or to increase the volume of drug in the syringe used to refill the reservoir. Either of these two scenarios would frequently result in undesirable waste of drug.